In packing technology finished consumer packages of non-returnable character which are manufactured from a material consisting of a carrier layer of cardboard or paper and outer and inner coatings of thermoplastics have been used for a long time. Material in these so-called non-returnable packages is often also provided with one or more layers of other material, e.g. aluminum foil or plastic layers of a different type than those mentioned here.
The composition of the packing material is selected to create the best possible protection for the product which is to be packed, while at the same time providing the package with sufficient mechanical strength to make possible a comfortable handling of the package. To achieve the required mechanical strength which affords protection for the contents and makes it possible for the package to be sufficiently rigid in its dimensions so that it can be handled and manually gripped without difficulty, the material in packages of this type is frequently provided with a relatively thick carrier layer of paper or cardboard. Such a carrier layer, however, is not airtight with respect to gases or liquids and the rigidity of the material is quickly lost when it is subjected to moisture or liquid. To impart to the material a good liquid tightness a thin coating of plastic material is provided, and, if the plastic material is a thermoplastics, it may also be used for sealing the plastic layers to one another by means of heat and pressure (so-called heat-sealing). Thus a packing container can be sealed and made permanent in its given shape by heat-sealing overlapping, thermoplastic material panels to one another in a tight and mechanically durable seal.
Non-returnable packages of the type described above are manufactured either from blanks punched out beforehand or from a continuous web which has been prepared with suitable decoration and with a pattern of crease lines facilitating the formation of folds. Packing containers are manufactured from a web by joining to one another longitudinal edges of the web in an overlap joint, so as to form a tube which subsequently is filled with the intended contents and is divided into closed cushionlike container units through repeated flattenings and transverse sealings of the tube at right angles to the longitudinal axis of the tube. Through appropriate fold-forming of the packing material in the tube the container units are converted to the desired geometrical final shape, usually a parallelepiped.
The problem with the abovementioned packages has always been the difficulty associated with creating an opening arrangement which is comfortable to handle and which functions satisfactorily, that is to say which can be opened readily without the use of a tool and which allows emptying of the contents in a uniform and well-defined jet.
One type of known opening arrangements up to now consisted of some form of perforation which extends through the outer plastic layer of the packing container and the carrier layer, whereas the inner plastic layer of the packing container is kept intact. The demand made on such an opening arrangement certainly is that it should be easy to tear the perforation when the package is to be opened, but the perforation should not be liable to be torn up during normal handling and transport of the package. It will be readily understood that these two demands are difficult to meet at the same time, since avoidance of inadvertent opening of the perforation during handling of the package implies that the perforation should not weaken the package wall to an excessive degree, which in turn means that greater force will be needed for tearing open the perforation when the package is to be opened. It also has been found that perforations of this kind may give rise to small leakages, which perhaps are not so great as to allow the contents to escape, but are still large enough to enable bacteria to penetrate and infect the contents of the package.
A somewhat more readily openable package is that which has been provided with an opening arrangement of the tearing strip (so-called pull-tab) type, Such an opening arrangement usually comprises a hole punched out in the container wall which is closed with the help of a tearing strip attached to the outside of the container wall and which is sealed to a plastic film covering the hole from underneath. The plastic film usually consists of the inner plastic coating of the packing material, but may be a separate plastic strip which has been sealed to the inside of the container wall along a liquid-tight sealing joint round the whole opening contour of the hole. Such packing containers are opened in that the tearing strip with the help of a readily grippable pull-tab or pull-ring is pulled upwards and backwards over the hole, as a result of which the firmly sealed plastic film, covering the hole from underneath, is stretched and torn off against the cut edge of the hole to expose a corresponding pouring opening through which the contents of the package can be emptied.
An opening arrangement similar to that described above is as a general rule easy to open, but the ability the contents to be poured in a desired coherent and well-directed jet is impaired by the fact that the plastic film adhering to the inside of the package often produces a somewhat uneven or frayed tearing edge around the pouring opening. One of the causes of the uneven tearing edge is that it is difficult to carry out the seal between the tearing strip and the plastic film in the area closest to the cut edge of the opening which means that as the outer tearing strip is pulled away, the plastic film is stretched and breaks sooner within this poorly sealed region than against the cut edge of the opening. A futher problem with this type of opening arrangement is that the plastic film torn away within the opening region exposes the cut edge of the opening so that the contents come into contact with, and are absorbed by, the cut edge during the pouring.